Hydraulic elevators include a hydraulic jack which is mounted in the hoistway pit and supports the elevator car. A pump unit supplies hydraulic fluid from a reservoir to the jack through a solenoid-operated valve that includes flow regulating pistons for selectively raising and lowering the car. The valve is, in turn, operated by a control system. The control system performs the functions of receiving hall calls and car calls, dispatching the car to the appropriate floors, stopping the car level with the floor landings, and opening and closing the doors. Part of the overall control system is a selector, which senses the position of the elevator car in the hoistway and determines slowdown and stopping points.
Traditionally, all of the control functions of a hydraulic elevator have been performed by relay circuitry centrally located in the machine room adjacent to the power unit. Car position signals are provided by switches mounted at appropriate locations in the hatchway. The switches are actuated by cams mounted on the car and the signals are brought to the controller by a hoistway riser.
A door operator mechanism is mounted on top of the elevator car. It includes a motor, pulleys and a linkage connected to the door, and cam-operated micro switches actuated at various points including the door open limit, door close limit, and door slowdown points. Switch signals are fed to the controller through wires from the hoistway. Thus, the controller is physically adjacent to some of the machinery it controls, but is remote from the door operator and to the external signals it requires.
Microprocessors possess a number of potential advantages over relay-based controls from the standpoint of system flexibility. It would be desirable, therefore, to replace the door operator relay controls in a hydraulic elevator with a microprocessor controller, provided that such a control could be employed with hydraulic elevator hardware in a cost effective manner.
As noted before, traditionally the controller and power unit are located in a machine room. The operating temperatures and vibrations of the power unit make the machine room a relatively inhospitable environment for delicate components such as microprocessors. It is not practical, then, to substitute a microprocessor control for relay circuitry without either taking special protective measures or utilizing components having higher specifications than that of typical industrial or consumer-grade components. This is undesirable from the standpoint of the higher costs involved.
Alternatively, as one manufacture has done, the microprocessor control may be relocated to another location such as on the car. However, the control circuitry in conventional hydraulic elevators is located in the machine room in order to be located close to the power unit, thereby minimizing the amount of power wiring. Relocating the control would require then additional wiring so that the microprocessor will still be able to communicate with the machinery and power supplies in the machine room and switches in the hoistway. To reduce installation cost and to improve reliability it is desirable to keep the amount of wiring to a minimum.
Each microprocessor has inherent limitations in terms of its input/output capabilities (number of I/O ports), processing capability, and speed. In any control system for an elevator, it is undesirable to have delays in processing and transmitting critical information, such as slowdown and stop signals, certain door control signals, and safety information. At the same time, it would be desirable from the standpoint of cost to minimize the number of dedicated terminals used by the central control for input/output with peripheral devices, to perform control functions using minimum microprocessor capability, and to perform critical decision-making functions with a minimum of delay.